In the design and testing of gas turbine engines, it is often desirable to take gas flow readings to obtain and/or validate data regarding the operation of the gas turbine engine or component rig. The so-called multi-hole pressure probe has been a standard technique for measuring mean flow angles, stagnation, and static pressures of the flow for over four decades. Generally, these probes make use of the known (through experiment or analysis) geometrical variation of all static pressure on fixed shapes (sphere, cylinder, wedge, etc.) which changes in a repeatable way as a function of that shape's orientation to the flow. Since the Mach number is a unique function of the ratio of stagnation to static pressure, it can also be derived from the pressures measured by such a probe. Up to two orthogonal flow angles as well as stagnation and static pressure can be deduced from pressures measured at four or five well-chosen locations on the probe (using five rather than four measurement locations generally improves the accuracy but requires a larger probe). Fewer measurements yield fewer flow variables. For example, if the probe size is a concern, then two measurements can be used to find either one flow angle or stagnation and static pressures. The static pressure ports on these steady state probes are usually connected to remote pressure transducers via long lengths of small diameter tubing.
The standard configuration for 3-D capable probes is a central hole surrounded by two pair of angled holes. These angled holes, which are configured to measure the pitch and yaw orthogonal angles, have classically been either a pyramid, sphere, or cone design or simply individual brazed tubes. Since there are only four independent quantities to be measured (two angles, speed and total pressure) it is possible to determine them with only four measurements of pressure (provided the four are independent). The advantages of a four-hole probe over a five-hole probe are that fewer measurements need to be made during operation and calibration of the probe.
To provide meaningful aerodynamic data in the context of measurements taken in an operating gas turbine engine or a component rig, multiple samples across a bladerow pitch (for example of a turbine or compressor section of the gas turbine engine) are preferred. This means the probe tip needs to measure less than about 0.100″ in all dimensions for use in small-class gas turbine engines, such as those that may be implemented on helicopters, light aircraft, and the like. One of the main difficulties in producing a 3-D yaw/pitch-type probe in a tip of the small size noted above is placing the holes accurately on the face and providing independent pneumatic tubes for the pressure signals. Standard manufacturing techniques such as drilling or electrical discharge machining (EDM) cannot produce probes of this type and complexity.
Accordingly, it is desirable to have an improved multi-hole probe that is small enough to take adequate measurements in small-class gas turbine engines. It is further desirable to provide improved manufacturing techniques capable of producing such multi-hole probes. Furthermore, other desirable features and characteristics of the inventive subject matter will become apparent from the subsequent detailed description of the inventive subject matter and the appended claims, taken in conjunction with the accompanying drawings and this background of the inventive subject matter.